Serotonin stimulates several components and complex functions of activation in lymphokine and IFNgamma primed macrophages. The effect is specific, dose related and antagonized by the specific serotonin receptor blockers spiperone and ketanserin, suggesting mediation by specific 5-HT receptors. This grant will further define the stage of activation induced by serotonin and analyze the mechanism of this induction. Mouse bone marrow macrophages, human peripheral blood mononuclear cells and two human macrophage cell lines will be assessed for degree of Ia expression, lysozyme and prostaglandin secretion, proliferation, phagocytosis, and tumoricidal ability. The specificity of the serotonin effect will be determined with specific serotonin antagonists. The mechanism by which serotonin exerts its activating effect will be studied by analysis of serotonin related membrane events. Binding of [H-3]-serotonin to whole cells and membrane preparations and blocking of binding by specific serotonin receptor antagonists will be studied. The effects of serotonin on voltage changes across the macrophage plasma membrane will be assessed using single cell patch-clamp techniques. Transduction of the membrane signal will be examined by assessment of serotonin induced phosphorylation of macrophage proteins. The effect of serotonin at the level of transcription will be studied by assessing changes in c-myc, c-myb and c-fos mRNA in serotonin treated cells. Results from these experiments will be used to construct a profile of the stage of activation induced by serotonin and to define the subcellular mechanism of induction of macrophage activation.